Ylide compounds using

An attempted synthesis of biotin using thiocarbonyl ylide cycloaddition was carried out (131,133,134). The crucial step involves the formation of the tetrahydrothiophene ring by [3 + 2] cycloaddition of a properly substituted thiocarbonyl ylide with a maleic or fumaric acid derivative (Scheme 5.27). As precursors of the thiocarbonyl ylides, compounds 25a, 72, and 73 were used. Further conversion of cycloadducts 74 into biotin (75) required several additional steps including a Curtius rearrangement to replace the carboxylic groups at C(3) and C(4) by amino moieties. 

The Wittig reaction is a C,C-forming olefin synthesis from phosphonium ylides and carbonyl compounds (see also Section 4.7.4). In more than 99% of all Wittig reactions, ylides of the structure Ph3P+—CH-—X (i.e., triphenylphosphonium ylides) are used. Therein, X usually stands for H, alkyl, aryl, or C02-alkyl and seldom for other substituents. 

To access substitution pattern of azuidinomitosene A, 116 the use of the isoxazole ring as a precursor of an azomethine ylide proved useful. Treatment of compound 117 with silver triflate and a cyanide salt afforded compound 118 <07JOC8506>. 

The third typical reaction of carbenes is combination with a nucleophile. Carbenes are electron-deficient species, so they combine with nucleophiles that have reactive lone pairs. Addition of a carbonyl O to a carbene gives a carbonyl ylide, a reactive compound useful for making furan rings by a 1,3-dipolar cycloaddition reaction (see Chapter 4). 

Sulfoxonium ylides are useful in the preparation of cyclopropane derivatives by reaction with a,p-unsaturated carbonyl compounds (see Chapter 10, p. 189). Sulfoxonium salts (26) are intermediates in the Moffatt oxidation (Scheme 15a) (see Chapter 5, p. 66), and they also undergo several other useful reactions (Schemes 15b-15d). The Pummerer rearrangement involves an oxosulfonium ylide intermediate (see Chapter 5, p. 68). 

The sulfur ylides 254 used in the stereoselective [2,3]-sigmatropic rearrangement are generated by copper(I)-catalyzed Doyle-Kirmse reaction of aryl sulfides 253 and diazo compounds bearing Oppolzer s camphor sultam auxiliary 252 in the presence of chiral diamine ligand S, S)-259 <05JA15016>. These intermediate ylides undergo spontaneous... 

Sulfur ylides are useful reagents in organic synthesis. The ylide is formally a zwitterion in which a carbanion is stabilized by interaction with an adjacent sulfonium centre. They are usually prepared by proton abstraction from a sulfonium salt with a suitable base or by reaction of a sulfide with an alkylating agent such as Me30+BF4 or a carbene formed, for example, by metal-catalysed or photolytic decomposition of a diazo compound (1.103). 

Another successful catalytic enantioselective 1,3-dipolar cycloaddition of Qf-diazocarbonyl compounds using phthaloyl-derived chiral rhodium(II) catalysts has been demonstrated [ill]. Six-membered ring carbonyl ylide formation from the a-diazo ketone 80 and subsequent 1,3-cycloaddition with DMAD under the influence of 1 mol % of dirhodium(II) tetrakis[M-benzene-fused-phthaloyl-(S)-phenylvaline], Rh2(S-BPTV)4 101 [112], has been explored to obtain the cycloadduct 102 in up to 92% ee (Scheme 31). 

Oxonium ylides are useful intermediates in organic synthesis, and their reactivity in multicomponent reaction has been explored by the in situ generation from diazoacetate derivatives, such as compound 35, with a metal catalyst, as depicted in Scheme 11.29. This reaction provided access to products 75 containing a quaternary stereogenic center, with the addition of TsOH as additional Brpnsted acid being crucial in order to accelerate the reaction and enhance the selectivity [78]. 

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